The present invention relates to a transfer system for an automobile having a sub speed change gear for selectively performing the high-speed and low-speed driving operations in the two-wheeled or four-wheeled driving mode and, more particularly, to a transfer system of this type adapted to prevent the racing of the speed reduction gear system including a counter gear when the sub speed change gear is set to the high-speed position.
Hitherto, as such a transfer system having a sub speed change gear to selectively perform the four-wheeled driving operation (hereinafter, referred to as a 4WD) and the two-wheeled driving operation (hereinafter, referred to as a 2WD), for example, a system as shown in FIG. 1 has been known.
In FIG. 1, reference numeral 10 denotes a transfer unit to selectively perform the 2WD and 4WD, and 12 indicates a sub speed change gear unit which receives the rotational motive power from a main speed change gear (not shown) and sets the operating mode to the high speed or low-speed operating mode. A main drive shaft 18 is rotatably attached in a casing 14 of the sub speed change gear 12 by a bearing 16. The rotational motive power from the main speed change gear is transferred to the main drive shaft 18. Subsequent to the main drive shaft 18, a main shaft 20 is coaxially and relatively rotatably attached in the casing 14 through a needle bearing 25. The main shaft 20 is rotatably supported to a casing partition wall 24 by a bearing 22. Further, the main shaft 20 penetrates inside of a casing 26 of the transfer unit 10 and is supported by a bearing 28 and thereafter, the main shaft 20 is taken out to the outside and extended to the side of a propeller shaft (the side of rear wheels).
A main drive gear 30 is fixed to the main drive shaft 18 of the sub speed change gear unit 12. A first counter gear 34 fixed to a counter shaft 32 is come into engagement with the main drive gear 30. A second counter gear 36 fixed to the counter shaft 32 is come into engagement with a speed change gear 40 relatively rotatably attached to the main shaft 20 through a needle bearing 38. The counter shaft 32 is rotatably supported by the casing 14 and partition wall 24 by bearings 45 and 55.
Therefore, the rotational motive power of the main drive shaft 18 is transferred through the main drive gear 30, counter gear 34, counter shaft 32, and counter gear 36 to the speed change gear 40, so that the speed is reduced.
A hub 42 having an outer peripheral spline is fixed to the position of the main shaft 20 between the main drive gear 30 and the speed change gear 40. A coupling sleeve 44 is come into engagement with the outer peripheral spline of the hub 42 so as to be slidable in the axial direction by the inner peripheral spline. Further, a clutch gear 46 is arranged on the left side of the hub 42. The clutch gear 46 is formed integrally with the main drive gear 30. A clutch gear 48 is arranged on the right side of the hub 42. The clutch gear 48 is formed integrally with the speed change gear 40.
The coupling sleeve 44 is moved in the axial direction by a shift fork (not shown) which is interconnected with the operation of a shift lever. When the shift lever is set to the high-speed position, the coupling sleeve 44 is come into engagement with the hub 42 and clutch gear 46 as shown in the diagram, thereby directly coupling the main drive shaft 18 with the main shaft 20. The rotational motive force from the main drive shaft 18 is directly transferred to the main shaft 20 without reducing the speed.
On the contrary, when the shift lever is set to the low-speed position, the coupling sleeve 44 is moved to the right and is come into engagement with the clutch gear 48 on the side of the speed change gear 40, thereby coupling the gear 40 with the main shaft 20. Thus, the rotational motive power from the main drive shaft 18 is transferred to the speed change gear 40 through the path consisting of the main drive gear 30, counter gear 34, counter shaft 32, and counter gear 36. Further, this power is transferred through the clutch gear 48, coupling sleeve 44, and hub 42 to the main shaft 20. Thus, the rotational motive power is reduced at the speed reduction ratios which are set by the engagement between the main drive gear 30 and the counter gear 34 and by the engagement between the counter gear 36 and the speed change gear 40. The speed reduced rotational motive power is transferred to the main shaft 20.
The transfer unit 10 will now be described. A hub 50 is fixed to the main shaft 20 which penetrates inside of the casing 26. A front driving sprocket gear 54 which is formed integrally with a clutch gear 52 is rotatably arranged on the left side of the hub 50 through a needle bearing 65. A coupling sleeve 58 is come into engagement with the outer peripheral spline of the hub 50 so as to be movable in the axial direction by the inner peripheral spline. The coupling sleeve 58 is moved in the axial direction in association with the motion of the shift lever which is set to the 2WD or 4WD position. When the shift lever is set to the 2WD position, the coupling sleeve 58 is moved to the right and disengages from the clutch gear 52, so that the sprocket gear 54 is disconnected from the main shaft 20. When the shift lever is set to the 4WD position, the coupling sleeve 52 is moved to the left and is come into engagement with the clutch gear 52 as shown in the diagram. Thus, the sprocket gear 54 is coupled with the main shaft 20 and is rotated integrally with the main shaft 20.
A front drive shaft 60 is rotatably supported by bearings 62 and 64 at the position which is away from the main shaft 20 by a predetermined distance. A sprocket gear 66 is fixed to the front drive shaft 60 and a chain 68 is wound between the sprocket gears 60 and 54.
Therefore, when the coupling sleeve 58 is come into engagement with the clutch gear 52 by setting the shift lever to the 4WD position, the rotational motive power of the main shaft 20 is transferred to the front drive shaft 60 through the hub 50, coupling sleeve 58, clutch gear 52, sprocket gear 54, chain 68, and sprocket gear 66. The front wheels are driven by the front drive shaft 60 and at the same time, the rear wheels are driven by the main shaft 20, so that the automobile enters the 4WD running state.
On the other hand, when the shift lever is set to the 2WD position, the coupling sleeve 58 disengages from the clutch gear 52 and the rotational motive power of the main shaft 20 is not transferred to the sprocket gear 54. Thus, only the rear wheels are driven by the main shaft 20. The automobile enters the 2WD running state.
However, in such a conventional transfer system, in the running state in which the sub speed change gear unit 12 is set to the high-speed position and the main drive shaft 18 is coupled with the main shaft 20, the main drive gear 30, counter gears 34 and 36, and speed change gear 40 which do not transfer the motive power race, so that there occurs such a problem that the engagement noises are generated by the racing of the gears.
On the other hand, there is also a problem such that the loss of motive power occurs in the driving system due to the unnecessary rotations of the main drive gear 30, counter gears 34 and 36, and speed change gear 40 at the high-speed position.